<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>JS打字小游戏</title>
    <style>
        body {
            padding: 0px;
            margin: 0;
        }

        #gameStage {
            width: 100%;
            height: 1000px;
            background-color: aquamarine;
        }
    </style>
</head>
<body>
<div id="gameStage"></div>
<script>
  /**
   * 字母
   * @param id
   * @param alphabet
   * @param posX
   * @param posY
   * @param size
   * @constructor
   */
  var it;//全局变量，用来接受定时器的返回值
  function Word(id, alphabet, posX, posY, size) {

    //初始化数据
    this.id = id || '';
    this.alphabet = alphabet || 'a';
    this.posX = posX || 0;
    this.posY = posY || 0;
    this.size = size || 64;


    // 新建
    this.create = function () {
      var str = '<span class="word" id="alphabet-' + this.id + '">' + this.alphabet + '</span>';
      var gameStage = document.getElementById('gameStage');
      gameStage.innerHTML += str;

      var divNode = document.getElementById('alphabet-' + this.id);
      divNode.style.position = 'absolute';
      divNode.style.fontSize = this.size + 'px';
      divNode.style.left = this.posX + 'px';
      divNode.style.top = this.posY + 'px';

    };

    // 重置.
    this.reset = function () {
      var divNode = document.getElementById('alphabet-' + this.id);
      divNode.style.display = 'none';
      this.moveTo(0, 0);
    };

    // 移动到指定点
    this.moveTo = function (posX, posY) {
      this.posX = posX;
      this.posY = posY;

      var divNode = document.getElementById('alphabet-' + this.id);
      divNode.style.left = posX + 'px';
      divNode.style.top = posY + 'px';
    };

  }

  /**
   * 导演类
   */
  var director = {
    alphabets: ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'],


    nodes: new Array(),

    /**
     * 逐帧运行
     */
    runFrame: function () {
        var _this=this;
      //更新已经产生所有点的坐标
      for (var index in this.nodes) {
        var node = this.nodes[index];
        if (node) {
          node.moveTo(node.posX, node.posY + 5);
          if(node.posY>window.innerHeight){//判断字母是否超出屏幕最下方

              alert('游戏结束！'+'score:'+scoreCounter.score);
              node.reset();
              window.clearTimeout(it);
          }
        }
      }
      //随机产生字母
      var r = Math.floor(Math.random() * this.alphabets.length);
      var w = new Word(new Date().getTime(), this.alphabets[r]);

      w.create();
      this.nodes.push(w);

      var posX = Math.floor(Math.random() * window.innerWidth);
      if (posX < 50) {
        posX = 100;
      }
      if (posX >= window.innerWidth - 100) {
        posX = window.innerWidth - 100;
      }


      w.moveTo(posX, 0);
    },

    /**
     * 开始游戏
     */
    start: function () {
      var _this = this;

      //监听键盘事件
      document.onkeydown = function () {
        var alphabet = String.fromCharCode(event.keyCode); //获取键盘敲中的字母
        for (var i = 0, len = _this.nodes.length; i < len; i++) {
          if(!_this.nodes[i]) {
            continue;
          }
          if (alphabet === _this.nodes[i].alphabet) {//如果键盘输入和屏幕的字母相同，则分数增1.
            _this.nodes[i].reset();
            scoreCounter.incScore();
            _this.nodes[i] = null;
          }
        }

        for(var index in _this.nodes){  // 遍历所有字母，判断是否相等，如果不相等，则分数减1，退出循环。
            var node=_this.nodes[index];
            if(alphabet!==node){
                scoreCounter.outScore()
                break;
            }
        }
      };
      //游戏主循环
       it=setInterval(function () {
        _this.runFrame();
      }, 500);

    },
  }

  /*
   * 游戏结束
   */



  /**
   * 计分器
   */
  var scoreCounter = {
    score: 0,
    incScore: function () {//分数增加
      this.score++;
    },
      outScore:function () { //分数减少
        this.score--;
      },
    getScore: function () {
      return this.score;
    }
  };
  console.log(scoreCounter);//显示分数多少
  director.start();

</script>
</body>
</html>